1. Field of the Invention
This invention relates to a method for continuously measuring changes with time in a physical property of various liquid and semisolid materials without destroying the original state thereof.
2. Description of the Prior Art
Conventionally, a physical property (e.g., coefficient of viscosity) of a liquid or semisolid material has been measured by rotating a cylinder or a sphere in a sample to be tested or by allowing a sphere to fall freely in the sample.
However, these methods have the inherent disadvantage that, where the sample is in a semisolid form, the sample itself is destroyed in consequence of the measurement. For example, in the case of a processed food whose viscosity changes in the course of processing, the greatest care must be taken in controlling the behavior of its viscosity, whether the foods may be liquid or semisolid. But, in measuring its coefficient of viscosity for the above-described controlling purpose, the internal structure of the processed food itself may often be destroyed. Accordingly, the physical property (e.g., coefficient of viscosity) determined by analysis of the measured results obtained with destruction of its internal structure will be useless for predicting changes in viscosity of the processed food which does not undergo any destruction or is destroyed at a quite different rate.
Moreover, where a physical property of materials (such as biological tissue and the like) whose properties change with time, the above-described methods involving destruction of the sample can only evaluate the physical property at a specific point of time and cannot predict its changes with time by any possibility. That is, changes in a physical property of such materials must be measured in real time and continuously.
In order to measure the degree of coagulation of raw milk in in the manufacture of cheese and yogurt without deforming the curd by the application of an external force or breaking it down, the present inventor previously developed a method for detecting changes in the degree of coagulation of milk which comprises placing a thin metal wire in milk being coagulated, passing an electric current intermittently or continuously through the thin metal wire, and measuring the increase in temperature of the thin metal wire with the lapse of time (Japanese Patent Application No. 92079/'83).
Although this method is useful in measuring the degree of coagulation of milk, it is of no practical use in measuring changes in a physical property of systems undergoing a wide range of changes or systems very sensitive to temperature (e.g., biological systems), because the temperature rise caused by the electric current flowing through the aforesaid thin metal wire may result in thermal destruction. Even when this method is used to measure the degree of coagulation of milk, the separation of whey from the curd may result because of the excessive heating caused by the electric current flowing through the thin metal wire.